Complex mixtures of said isomers are disclosed in U.S. Pat. No. 3,312,592; J. Med. Chem. 13, 169 (1970) or Chem. Abstr. 79, 126411j (1973) as .beta.-adrenergic blocking, sympatholytic and adrenolytic agents for the treatment of prophylaxis of coronary artery diseases. Said mixtures of at least eitht erythro- and threo-diastereomeric forms cannot be separated easily. Due to our new process for suitably substituted erythro forms of 2-(1-hydroxyethyl)-1,4-benzodioxan intermediates it is possible to obtain simple mixtures of said isomers, which can be separated more readily.
Surprisingly, it was found that only the above-specified R, S, R-diastereomers exhibit said valuable pharmacological effects, whereas the S, R, S--; S, R, R-- and R, S, S-- analogs are merely contributing to their side effects, e.g. toxicity.